The present invention relates to a chuck. More particularly this invention concerns a collet chuck for attachment to a mounting collar of a tool or of a workpiece to be machined.
A standard collet chuck for attachment to a mounting collar of a tool or workpiece has a body formed centered on an axis with a forwardly open socket shaped to coaxially receive the mounting collar. A collet inside the body has a plurality of jaws with front ends that project axially forward into the collar. The jaws can rock to move the front ends radially outward to engage behind an axially forwardly directed shoulder of the collar and thereby lock the collar to the chuck body. Each jaw can pivot in the body about a respective axis extending in a plane perpendicular to the axis and offset therefrom. An axially displaceable cam sleeve inside the body has a radially outwardly directed front cam surface engageable with front inner faces of the front ends of the jaws and a radially outwardly directed rear cam surface engageable with rear inner faces of rear ends of the jaws. Thus, when displaced axially rearward, the cam sleeve spreads the front ends of the jaws to hold the workpiece and, when displaced axially forward, rocks these front ends inward to release the workpiece.
In copending application Ser. No. 09/930,922 such a chuck is described which has, in order to maintain the jaws at a perfect angular equispacing to eliminate vibration and throw on high-speed rotation, radially outwardly projecting and axially extending ribs extending from the setting sleeve and each received in a respective one of the slots between the jaws. Thus the jaws are positively held at the necessary spacing so they will move only radially. This system works fairly well, but the setting sleeve is somewhat difficult to manufacture and to fit together with the jaws to form the collet subassembly.
It is therefore an object of the present invention to provide an improved collet chuck.
Another object is the provision of such an improved collet chuck which overcomes the above-given disadvantages, that is which can operate at very high rotation speeds without vibration and which is of simple and inexpensive construction.
A collet chuck for holding a mounting collar of an object to be rotated has according to the invention a chuck body centered on and rotatable about an axis and formed with an axially forwardly open socket shaped to receive the collar. A plurality of jaws in the socket have front ends engageable inside the collar in the socket and each formed with a radially inwardly directed planar front face. The jaws are angularly spaced and defining axially extending and radially inwardly open slots. A setting sleeve has a front cam surface formed with respective planar radially outwardly directed front facets engageable with the front faces of the jaws so that the sleeve can cam out the front ends to lock the jaws to the collar in the socket.
Thus with this system the planar engagement of the angularly equispaced facets of the setting sleeve that occurs each time the chuck is clamped to a workpiece or tool automatically angularly positions the jaws perfectly. In addition the surface contact ensures good force transmission and low wear.
In accordance with the invention the chuck body is formed axially rearward of the socket with a radially inwardly open groove centered on the axis and each jaw has a rear end received and radially displaceable in the groove and formed with a radially inwardly directed planar rear face. The setting sleeve has respective planar radially outwardly directed rear facets engageable with the rear faces of the rear ends of the jaws so that the sleeve can cam out the rear ends to move the front ends radially inward and axially clear of the collar in the socket.
The ribs in accordance with the invention are of an angular dimension increasing outward from the axis. In addition a spring engaged around the rear ends of the jaws urges the jaw front ends radially outward. The rear ends form a radially outwardly open groove receiving the spring and the spring has spacer blocks engaged between the jaws and braced angularly against the jaws so that the spacer blocks angularly space and separate the jaws. Thus prior to assembly of the chuck, the spring holds the jaws at the desired angular spacing.
The sleeve according to the invention is formed axially rearward of the rear cam surface with respective planar rearmost facets extending parallel to the axis and engageable with the jaw rear ends to retain same in a freeing position with the jaw front ends shifted inward. Thus when the sleeve is shifted far enough forward to engage these rearmost facets against the rear inner faces of the jaws, the chuck will hold in this position.
The groove has an axially rearwardly directed flank engaging the jaw rear ends. This flank has a radially outer portion lying substantially in a plane perpendicular to the axis and a frustoconical radially inner portion inclined at about 10xc2x0 to the plane. This facilitates rocking of the jaws and assembly of the device.
The mounting collar in accordance with the invention has an axially forwardly directed shoulder and the jaw front ends each have an axially rearwardly directed shoulder engageable axially with the collar shoulder.